Sulfonation process



Patented Sept. 26, 1950 SULFONATION mocnss Raymond W. Mattson, Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application March 28, 1945, Serial No. 585,347

6 Claims. (Cl. 260-504) This invention relates to the sulfonation of organic compounds and especially to a method for sulfonating petroleum fractions with gaseous sulfur trioxide.

The sulfonation of organic compounds is becoming of increasing importance in our daily life. For example, many of the synthetic detergents which are being employed as substitutes for soap are prepared by processes involving sulfonation of alcohols and esters, and even of hydrocarbons of the aromatic hydrocarbon type. Sulfonation of non-aromatic hydrocarbons is also of importance, not so much from the soap substitute standpoint, but for the purpose of preparing additives which enhance the value of lubricants such as motor oil.

In the sulfonation of petroleum fractions, which contain hydrocarbons of both aromatic and non-aromatic types, it has been found that sulfonic acids of two different types are formed. The acids of one type are called green acids, and

. the acids of the other type are called mahogany acids, these names being descriptive of the colors of the two products.. The green acids are predominantly water soluble, and when freed of contaminating oil, are useful in the preparation of detergents such asthe soap substitutes above and other additives for use in aqueous media. The mahogany acids are predominantly oil-soluble, and need not be purified to the extent of removing all the unreacted oil, when employed as additives for oily media such as lubricating oils and greases. The process of this invention pertains particularly to the sulfonation of petroleum fractions for the preparation of lubricating oil additives. The broad aspects of the invention, however, are applicable to the sulfonation of any organic compound with sulfur trioxide. In this regard, the expression sulfonation" as employed herein is meant to include any reaction between the organic compound and sulfur trioxide, and includes sulfation as well as sulfonation.

As additives for lubricating oils, the mahogany acid salts of the alkaline earth metals (especially Ca, Sr and Ba) are preferred, although sulfonate salts of other polyvalent metals may also be employed, such as Zn. Al, Pb, and the like, as well as those of mcnovalent metals such as Na and K. It is desirable that these additives be prepared in the form of a liquid concentrate,

which contains more than 30% by weight and preferably more than about 50% by'weight of the sulfonate dissolved in oil. In this form the additive is most readily measured and dissolved 2 in the lubricating oil in which it is to be used. Concentrates containing lower proportions of suifonates are less desirable, since the oil associtreated with fuming sulfuric acid, washed with water, and neutralized with caustic soda. The small amount of sodium sulfonate remaining in the oil has been extracted with alcohol and transferred to a second oil base, or alternatively, concentrated by means of alcohol extraction to obtain a concentrate containing about 60% of sodium sulfonate. This product has then been metathesized, with calcium chloride for example,- to obtain sodium chloride and a calcium sulfonate concentrate which, when purified to remove excess inorganic salts and water, was ready for use.

It is an object of this invention to provide a much simpler process than the above, whereby the extraction or concentration steps are eliminated. and a concentrate containing more than 30% by weight, or even more than 50% by weight in many instances, of sulfonate is produced directly. It is a further object of this invention to eliminate the metathesis step and obtain calcium sulfonate or any other desired sulfonate directly. from the sulfonic acid stock. Further objects are to employ gaseous sulfur trioxide instead of fuming sulfuric acid as the sulfonating agent, and to employ it in a novel manner. Other objects will appear below.

Sulfur trioxide has been employed as a sulfonating agent in the past, by bubbling sulfur trioxide-containing gases through a relatively large mass of the oil to be sulfonated, with or without agitation. It was found, however, that in this mode of operation there was great difficulty in obtaining a high yield of oil-soluble or mahogany sulfonates of good quality for use as lubricating oil additives. Under mild conditions of low temperature and low sulfur trioxide concentration, many of the most desirable stocks were not sulfonated to an appreciable extent,

and when more strenuous conditions of sulfonawas generally found necessary therefore, when using this method of the prior art, to employ stocks of relatively low molecular weight, such as B. A. E. '10 grade or lighter, and of high aromatic content, which stocks were more readily sulfonated; but it was found that the additives thus prepared, although suitable for use in aqueous media, were not suitable as additives for lubricating oils.

It has now been found that organic compounds may be sulfonated much more effectively with sulfur trioxide if the organic compounds are dispersed in the form of small particles, and the dispersed particles are contacted with gaseous sulfur trioxide. In a preferred form of the invention a gaseous stream comprising sulfur trioxide is employed to act as both the dispersing and the sulfonating means, by directing the gaseous stream in the form of a let, on a liquid stream comprising the organic compound, as it issues from a nozzle, in such a way as to cause a fine dispersion of the latter stream. By employing this method of sulfonation, it has been found possible to obtain high yields of mahogany sulfonic acids from stocks which could not be appreciably sulfonated by bubbling sulfur trioxide-containing gases through them. Sludge losses are low and the quality of the product as an addition agent for lubricating oils is excellent. The product, after removal of the sludge, may be directly neutralized with lime or calcium carbonate to obtain calcium sulfonate, or with an alkaline compound of any other metal as desired, and the concentration of the sulfonate in the finished concentrate is sufiiciently high so that 'no extraction with alcohol, etc, is necessary.

The complete process of this invention may be illustrated by the attached drawing, which shows a specific example of one method of operation. The sulfonation stock in this case was a petroleum lubricating oil fraction prepared by vacuum distilling a waxy crude from the Santa Fe Springs, California field to obtain a fraction in about the S. a. E. 40 range, dewaxing this product to reduce its pour point to about F., solvent extracting the dewaxed oil with phenol to obtain an extract fraction comprising about 60% by volume of the total, and solvent treating this extract with furfural to obtain a rafiinate fraction comprising about 35% of the phenol extract.

Referring to the figure, a blend consisting of about 67% by volume of the above-described feed stock and about 33% by volume of petroleum naphtha of about 140 F. to 200 F. boiling range,

was introduced into reaction chamber is through line I and valve l5, at a rate of about 300 ml. per hour. This reactor was operated at about atmospheric pressure. A gaseous stream containing about 6 mol per cent sulfur trioxide was also introduced into reaction chamber l3 through line l0 at a rate of about 340 liters per hour. This gaseous stream was directed in the form' of a jet against the stream of stock entering through line H in such a manner that the stock was dispersed into small particles. The gaseous stream served to sulfonate these particles, producing a liquid mass containing sulfonicacids, some unreacted oil, and sludge; and residual spent gases containing small amounts of sulfur trioxide and sulfur dioxide.

The gaseous stream entering through line l0 consisted of a mixture of sulfur trioxide and air, and was obtained by air stripping of fuming sulfuric acid in chamber l which was a packed column which was heated by means of a steam jacket, not shown. In this operation fuming suli'uric acid containing about sulfur trioxide was introduced into chamber I through line 2 and valve 3 and was contacted by a stream of air introduced through lines l1 and 6 and valves l8 and I at the bottom of the chamber. The air stream served to strip the sulfur trioxide from the fuming acid and carry it through lines 8 and I0, pump l I, and valve l2 into the reaction chamber ll. The spent acid constituting sulfuric acid substantially free from sulfur trioxide was withdrawn from chamber I through line 4 and valve 5.

The spent gases resulting from the reaction in chamber l3, as described previously, were withdrawn through line 83 and valve at. These gases could also be recirculated to chamber I through line l6 and valve 65 and line B and valve 1 and used to strip additional sulfur trioxide from the fuming acid.

The above liquid mass comprising products of ---sulfonation was withdrawn from the bottom of reaction chamber I3 through line I8 and valve 20. This mass was then mixed with about five times its volume of naphtha entering through line 24 and valve 25. The resulting mixture was pumped through pump 2| and valve 22 to settling chamber 23. In this vessel the slud e was allowed to separate by settling and was withdrawn through line 28 and valve 21, and the diluted oil-sulfonic acid mixture was withdrawn through line 28. In line 28 it was mixed with a neutralizing agent, calcium carbonate suspended in an aqueous solution containing about 10% calcium chloride, which was introduced through line 29 and valve Ill, and the mixture was discharged into settling chamber 3|. The amount of neutralizing agent employed was slightly more than that necessary to provide theoretically complete neutralization, and resulted in a product mixture having a pH of about 7. The aqueous phase was settled and withdrawn through line 32 and valve 32 and the partially neutralized oil was withdrawn through line 24. Additional neutralizing agent, calcium hydroxide suspended in water, was introduced into line 34 through line 35 and valve 36 in an amount sufllcient to raise the pH of the mixture to about 8, and the completely neutralized mixture was discharged into vessel 21. The aqueous phase was settled and withdrawn from vessel 31 through line 38 and valve 39 and the oil phase containing a small amount of dissolved water and dissolved and suspended inorganic salts, was withdrawn through line 40, pump 4| and valve 42, heated in heater 4! and discharged into fractionating column 44. In this column the water, together with some of the naphtha diluent, was distilled overhead through line and valve 46. The water-free oil phase remaining was withdrawn from the bottom of the column through line 41 and valve 48 and discharged into filter 49 where the insoluble matter was separated from the oil and withdrawn through line 50 and valve 5|. The thus purified oil and naphtha solution was withdrawn through line 52 and pumped by means of pump 53 through valve 54 and heater 5 into distillation column 58. In the distillation column the naphtha diluent was vaporized and taken overhead through line 59 and valve 60 with the aid of some steam introduced through line 51 and valve Bl, and

accuses sulfur trioxide stream through the stock, the final concentrate obtained as a product contained only about one-tenth as much calcium sulfonate as the above product. It is believed that the fact that in the process of this invention the particles of the oil to be sulfon-ated are present in a fine state of division and present a large exposed surface area per volume of oil enables the sulfur trioxide to contact the particles more thoroughly and thus provide a greater degree of reaction. Surface to volume ratios over 100 are easily c-btainable by dispersion into droplets of moderate size, and ratios over 1000, obtained by finer dispersion, are preferred. These ratios apply where the measurements are made in centimeters and are therefore in units of reciprocal centimeters. It is also believed that such operation provides for a more selective reaction, 1. e., a reaction involving introduction of one or possibly two sulfonic acid groups into a large proportion of the hydrocarbon molecules, without too much undesirable side-reaction involving polysulfonation, oxidation, cracking, polymerization, and the like. This may be due in part to the fact that the above large surface to volume ratio exists only for the short time during which the oil particles are traveling between the nozzle and the wall of the reactor. In the specific example above, this contact time" was about 0.4 second. It should be less than about seconds in any case, and prefer-.

ably less than 0.5 second.

The sulfonation reaction may be controlled by control of the size of the dispersed particles and the method of dispersion, by control of the proportion of sulfur trioxide and the use of modifiers in the gaseous stream, by control of the temperature and pressure of the reaction and by the use of diluents for the oil. It may also be controlled to some extent by the size of the reaction chamher and the rates of introduction of the feed stock and sulfur trioxide streams. As regards the state of division, more complet sulfonation may be obtained by using extremely fine dispersion of the particles .as b the formation of a fog. It is not necessary, however, that such extreme sub-division be attained, but only that the organic feed stock be broken up into discrete particles or droplets. Excellent results were obtained in the above example by introducing the oil and gaseous streams respectively into reactor l3 through nozzles having diameters at the tip of about 0.053 cm. and 0.034 cm., respectively. These nozzles were placed at right angle to each other and about 0.15 cm. apart. However, the nozzles may be directly opposed, i. e., at a 180 angle, or at any other angle. They may also be co-axial, with the one stream' entering through an annular space surrounding the other nozzle. Eductors or spray nozzles of any kind may be employed, as long as the feed stock is dispersed into discrete particles at or before the time of contacting the sulfur trioxide. a

The reactor may be operated by sub-atmospheric or super-atmospheric pressures to further The ratio of sulfur trioxide to sulfonation feed stock should be maintained at a constant value within the range of about 25% to 150% and preferably between 35% and of the weight of feed stock, to obtain the best product for use as a lubricating oil additive. For other purposes, howeverthis ratio may vary within wider limits depending on the degree'of sulfonation desired.

The gaseous stream employed in the above example contained about 6 mol per cent of sulfur trioxide, the rest being air. ever, to use gaseous streams containing higher proportions of sulfur trioxide, up to about 25 mol per cent, or greater, and it is also possible to use streams containing as little as 0.1% or less of sulfur trioxide. It is-preferred, however, from the standpoint of efficiency of operation and quality of product to employ streams containing between about 4 and 8 mol per cent sulfur trioxide.

It has been found that the presence of sulfur dioxide in the sulfur trioxide stream is somewhat beneficial so that the recirculation indicated in the drawing, via line l6 and valve 65, is a preferred mode of operation. It has also been found that the presence of oxygen in the stream, resulting from the use of air or pureoxygen as a dilruent, has been benficial. It has also been found that other modifiers may be employed to advantage, such as oxides of nitrogen or light-hydrocarbon gases. These may be introduced through line 9. It is preferable that the gaseous stream contains no substantial amount of water, however, although a small proportion of entrained sulfuric acid may do little harm. Oxygen and a catalyst may also be employed in chamber l to convert at least part of the sulfur dioxide to sulfur trioxide, when the recirculation system is employed. The effect of the size of the container and the rate of introduction of the streams controls the time of contact between the finely divided particles and the gaseous stream, and will be controlled in accordance with the'type of stock to be sulfonated and the degree of sulfonation desired.

The stock to be sulfon-ated is of considerable importance in determining the value of the product for preparing sulfonate concentrates to be used as lubricating oil additives. It is desirable that stock should have a viscosity greater than about 200 seconds (Saybolt Universal) at F. It is also desirable that the stock contain hydrocarbons which do not include any appreciable proportion of olefin hydrocarbons and which are not i it is desirable to employ a stock obtained as an intermediate fraction or heart out separated from a lubricating oil stock by a solvent fractionation process employing selective solvents such as phenol, furfural, sulfur dioxide, and the like. Such a fraction may be obtained from almost any lubricating oil stock but the yield will vary with type of stock employed. Fractions having a viscosity gravity-constant (defined by Hill and Coates in the Journal of Industrial and Engineering Chemistry, vol. 20 (1928) p. 641, in the range of'about .80 to .92 and preferably in the range of about .85 to .90 have been found to be particularly suitable, especially if they are homogeneous, i. e., if

It is possible, howi'onic acids.

7 they contain not more than about 20% of mate rial having a V. G. C. outside these desired ranges. The stock employed in thespecific example above had a gravity of 19.3 A. P. I., a viscosity at 100 F. of 3237 S. S. U., a viscosity at 130 F. of 980 S. S. U., and a viscosity gravity constant of 0.869. It was diluted with naphtha for the purpose of making it easier to pump and to disperse. Such dilution is not necessary, however, and smaller or larger proportions of diluent may be employed. As mentioned previously, part or all of the diluent may comprise a volatile relatively inert material such as propane, butane, or even sulfur dioxide or the like, which is vaporized in the reaction zone to provide temperature control.

Even though some diluent is present in the feed stock, it is usually desirable to add additional diluent, as through line 24, before settling the sludge from the sulfonation reaction product. This sludge contains undesirable products of side reactions as well as some sulfonic acids, and in some instances tends to separate from the oil very reluctantly. In any case, the addition of the diluent aids materially in making the settling of the sludge more rapid and more complete. The amount of the diluent employed should be between about 1 and about 5 times the volume of the oil sulf'onated. It has also been found that the addition of small amounts of water, such as about 5% to about by weight of the sulfonating agent is of definite value in aiding the sludge settling. The addition of water also tends to reject some of the sulfonic acids dissolved in the sludge into the oil phase, and this increases the recovery of sul- Thls does not reduce the value of the sulfonate concentrate product as a lubricating oil additive unless too much water is employed. Amounts between about 5% and 10% of the weight of the sulfonating agent are preferred.

In the process shown in the drawing two stages of neutralization are shown and this is frequently of advantage in view of the fact that careful control of the pH in the neutralization of the mixture is essential to provide for eflicient settling of the aqueous phase and the insoluble material from the neutralized product. The most efficient settling is realized at relatively low pH values such as about 5 to 7 /2, and poor settling is obtained at pH values above about 9. It is advantageous, therefore, to employ a two-stage neutralization, using in the first stage slightly less than the theoretical amount of a strong neutralizing agent such as a hydroxide, or an excess of a weak neutralizing agent such as a carbonate, so as to obtain a pH therein of about 5 to 7 /2, resulting in ready settling of the bulk of the aqueous phase and any insoluble salts formed; and then adjusting the pH to the preferred range of about 7 /2 to 8V. in the second stage. Different neutralizing agents may be employed in the two stages. For example, for preparing calcium sulfonate as in the illustration, lime may be used in the second stage and calcium carbonate in the first. Salts such as calcium chloride may also be employed in the first stage. It is also possible to employ either lime or calcium carbonate in the first stage and make the final adjustment in the second stage with caustic soda or sodium carbonate. If sodium sulfonate is desired as a product instead of calcium sulfonate, it is also convenient to employ sea water as the neutralizing agent for the first stage and caustic soda ash or the like as a neutralizing agent for the second stage.

tion. When calcium sulfonate is the desired.

product, lime suspended in water is the preferred neutralization agent, and the amount used is preferably controlled to obtain a product having a pH of about 8. Other neutralizing agents such as those described above may also be used alone or in mixtures, to provide a neutral product having a pH preferably between about '7 and 9. For example, a slurry containing 0.8 equivalents of calcium hydroxide and 0.3 equivalents of calcium carbonate (based on the acidit to phenolphthalein of the sludge settled acid oil) suspended in an aqueous solution containing 10% by weight of dissolved calcium chloride, is a very satisfactory neutralizing agent. The temperature during the neutralization step should be between about F. and 200 F. preferably between about 180 F. and 200 F. in order to obtain efficient neutralization.

The purification step involves removal of water dissolved in the oil-sulfonate concentrate as well as removal of the'insoluble solid material and inorganic salts formed in the neutralization as described above. It is usually found that the presence of dissolved water. will result in the presence of dissolved inorganic salts in addition to the undissolved salts. These dissolved salts are precipitated when the water is removed, so that it is desirable to remove the water before removing the solids. This is done most easily by distillation as shown in the drawing. A preliminary wash with sodium chloride solution such as sea water is also beneficial in converting inorganic sulfates to chlorides which are less objectionable. The removal of the precipitated and undissolved inorganic salts from the dehydrated sulfonate concentrate may be accomplished either by filtration as indicated in the drawing, or by centrifuging or in many instances, by merely settling. The diluent recovered from the clarified product in'the final distillation process may be recycled to be used again. This diluent may be naphtha or any other reasonably volatile hydrocarbon or petroleum fraction or may be any other inert volatile solvent, such as carbon tetrachloride or the like.

The utility of the sulfonate concentrate produced by the process of this invention may be shown by the following examples wherein a lubricating oil of S. A. E. 30 grade having a gravity of 29.1 A. P. I., a viscosity of 540 S. S. U. at 100 F. and viscosity index (defined by Dean and Davis in Chemical and Metallurgical Engineering vol. 36 (1929) p. 618) of 90 and containing a conventional antioxidant was employed as a base stock to which a calcium sulfonate concentrate prepared according to the process of this invention was added. The proportion of the concentrate added was sufficient to yield a product having a calcium sulfate ash value (see below) of 0.21% by weight. It was found that when this oil was tested in a heavy dut Diesel engine, the engine was operated satisfactorily for a period of 480 hours, at the end of which time the general cleanliness of the combustion chamber, piston and other parts of the engine was excellent. In similar tests employing the same base stock without the additive, serious deposition of sludge and carbon on the combustion chamber and piston walls resulted within a few hours of operation.

Similar tests have been conducted in smaller Lauson engines, in which the cleanliness of the engine was given a numerical rating between and 100%, the 100% value indicating a perfectly clean engine. This numerical value was called the detergency rating ofthe oil. It was found that the presence of twice the above amount of the sulfonate additive of this invention increased the detergency rating of an oil such as the above from about 58% to about 80%. Similar additives prepared from non-homogeneous stocks of lower viscosity b the processes of the prior art actually reduced the detergency rating under similar circumstances only from about 58% to about 55%.

In the Lauson'engine tests, corrosion sensitive alloy bearings such as cadmium-silver or copperlead bearings were used in the engine, and their loss in weight due to corrosion during the test operation was measured. It was found that when oils containing sulfonates prepared from high viscosity stocks according to the process of this invention were employed, the bearing corrosion was less than when employing similar oils containing similar sulfonates prepared from lower viscosity stocks according to processes of the prior art.

Data of the above type have shown clearly that the sulfonate additives prepared according to the process of this invention are of outstanding merit for the preparation of superior lubricating oils. The amount of additive employed should be sufficient to obtain a proportion of metal sulfonate in the finished oil which need not exceed about although proportions up to about 50% may be used in certain instances.

The calcium sulfate ash value referred to above is the value obtained by heating a weighed sample of the calcium sulfonate-containing oil to be tested, in the presence of sulfuric acid, to obtain a residual ash of calcium sulfate, and expressing the result in terms of per cent by weight of the oil tested. A rough approximation of the per cent of calcium sulfonate in a calcium sulfonate concentrate prepared from a preferred lubricating oil stock according to the methods of this invention as described above, may be obtained by multiplying the calcium sulfate ash value by about 7 or 8. For other sulfonates, or for more accurate data, analyses involving extraction of the sulfo- Y nate are necessary.

Modifications of this invention which would occur to one skilled in the art are to be considered as part of the invention as defined in v Icon oils which comprises dissolving them in a volatile inert hydrocarbon diluent, atomizing the solution to form a fine spray, and contacting the spray with a gas comprising sulfur trioxide for a timeless than about 5 seconds at a temperature not greater than about 170 F.

3. A method for sulf onating a petroleum lubricating oil stock which comprises directing a gaseous stream comprising sulfur trioxide, in the form of a jet, against a stream of said stock issuing from an orifice, in such a manner as to atomize said stream of stock to form particles having a surface to volume ratio greater than about reciprocal centimeters and sulfonating the particles formed by subjecting them to contact with said gaseous stream for a time less than about 5 seconds at a temperature not greater than about F.

' 4. A method for sulfonating a petroleum lubricating oil extract fraction which comprises atomizing and sulfonating said fraction by means of a gaseous stream comprising sulfur trioxide for a time less than about 5 seconds at a temperature not greater than about 170 F.

5. A method according to claim 6 in which the gaseous stream comprises sulfur trioxide, sulfur dioxide, and oxygen.

6. A continuous process for sulfonating a petroleum lubricating oil stock which comprises atomizing and sulfonating said stock by means of a gaseous sulfonating agent comprising sulfur trioxide, sulfur dioxide, and oxygen for a time less than about 5 seconds at a temperature not greater than about 170 F., separating from the reaction product a gaseous fraction comprising sulfur dioxide, passing said fraction into contact with fuming sulfuric acid in the presence of oxygen so as to regenerate additional sulfonating agent, and sulfonating additional stock therewith.

RAYMOND W. MA'I'ISON.

REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number Name Date 1,896,470 Steik Feb. 7, 1933 2,187,244 Mills Jan. 16, 1940 2,205,924 Frame June 25, 1940 2,234,005 Loane Mar. 4, 1941 2,266,325 Lazar Dec. 16, 1941 2,285,390 Brandt Jan. 9, 1942 2,307,743 Liberthson Jan. 12, 1943 2,361,476 Higbee Oct. 31, 1944 2,385,475 Sconce et a1 Sept. 25, 1945 2,395,713 Barbour Feb. 26, 1946 2,413,311 Cohen Dec. 31, 1946 FOREIGN PATENTS Number Country Date 553,598 Great Britain May 27, 1943 

1. A METHOD FOR SULFONATING HYDROCARBON FRACTIONS WHICH COMPRISES CONTACTING SAID FRACTIONS IN THE FORM OF A FINE SPRAY FOR A TIME LESS THAN ABOUT 5 SECONDS AT A TEMPERATURE NOT GREATER THAN ABOUT 170*F., WITH A GAS COMPRISING SULFUR TRIOXIDE. 